The histone H1°/H5 variant and terminal differentiation of cells during development of Xenopus laevis

The maintenance of the differentiated condition is supposed to be associated with the presence of a histone of the H1(0)/H5 subclass. If the H1(0)/H5 variant has an important role in differentiation distinct from that of H1, it should display differential expression in time and position during development. Here we report that this prediction is verified during Xenopus laevis development, in which tadpoles exhibit a very characteristic, developmentally regulated pattern of histone H1(0)/H5 expression that is different for the derivatives of each embryonic germ layer. However, the pattern of appearance of this variant during development does not reflect a simple correlation between its presence and the state of differentiation. Therefore, these results are pertinent to current ideas on differentiation and the involvement of lysine-rich histones in the repression of eukaryotic genes.     

Localization of c-ERB A proteins in rat liver using monoclonal antibodies

Monoclonal antibodies were raised against the nuclear thyroid hormone receptors encoded by c-ERB A genes and against a purified nuclear receptor fraction. These antibodies recognize the c-ERB A protein in nuclear extracts from rat liver and are able to compete with thyroid hormone in Scatchard analyses. In sections of rat liver they react with all the hepatocyte nuclei as well as with the cells of the hepatic bile ducts. Comparison with another putative T3 receptor antibody, described previously, showed that distinct 57 kD proteins with a different cellular distribution were recognized.     

Early indicators of exocrine pancreas carcinogenesis produced by non-genotoxic agents

In the past 40 years the incidence of pancreatic cancer in many Western countries had increased. Since no single factor responsible for the development of pancreatic cancer has been identified, it is believed that non-genotoxic factors may play an important role in the pathogenesis of this highly fatal form of cancer. Focal abnormalities of acinar cells, referred to as atypical acinar cell foci or nodules, occur spontaneously in rats and some other species. Their incidence increases with age from zero at birth to about 75% in 2-year-old rats. These spontaneous lesions have a phenotype that cannot be distinguished from the putative, atypical preneoplastic, acinar cell foci induced in rat pancreas by the carcinogen azaserine. Unsaturated fat (corn oil) has been found to increase the incidence of atypical acinar cell nodules and adenomas in the pancreas of non-carcinogen-treated rats without influencing the weight of the pancreas. Furthermore, unsaturated fat has a specific promoting effect on the growth potential of atypical acinar cell foci and nodules induced in rat pancreas by azaserine, resulting in an increase in the number and size of these lesions. Rats fed raw soya flour or trypsin inhibitors develop an enlarged pancreas as a result of hypertrophy and hyperplasia. They also develop acidophilic atypical acinar cell foci and nodules, adenomas and adenocarcinomas after being fed full-fat raw soya flour for 2 years. It may be concluded from the observations in rat pancreas that non-genotoxic compounds or conditions that enhance pancreatic growth may be classified as non-genotoxic pancreatic tumour promoters. The observations with corn oil, however, indicate that there may be non-genotoxic compounds that specifically enhance growth of spontaneous initiated atypical acinar cell foci without causing hyperplasia of the pancreas. The possible mechanisms whereby unsaturated fat and trypsin inhibitors exert their effects on exocrine pancreatic carcinogenesis are discussed.     

Effect of the specific cholecystokinin-receptor antagonist loxiglumide on bombesin stimulated pancreatic enzyme secretion in man.

We have investigated the effects of the specific cholecystokinin (CCK) receptor antagonist loxiglumide on basal and bombesin stimulated pancreatic enzyme secretion, bilirubin output and plasma CCK release in six healthy subjects. The data were compared with those obtained in control experiments where saline was infused instead of loxiglumide. Basal amylase output (4.7 +/- 0.8 kU/45 min), trypsin output (2.9 +/- 0.8 kU/45 min) and bilirubin output (7.7 +/- 2.8 mmol/45 min) gradually declined during infusion of loxiglumide to values of 1.3 +/- 0.3 kU/45 min, 0.5 +/- 0.1 kU/45 min and 0.4 +/- 0.0 mmol/45 min, respectively, reaching statistical significance (P less than 0.05) in the 30 to 45-min period after the start of the loxiglumide infusion. In the control experiments saline infusion failed to influence basal amylase, trypsin and bilirubin output, while bombesin stimulated amylase output from 4.7 +/- 0.8 kU/45 min to 25.1 +/- 5.1 kU/45 min (P less than 0.05), trypsin output from 2.9 +/- 0.8 kU/45 min to 11.6 +/- 2.0 kU/45 min (P less than 0.05) and bilirubin output from 7.7 +/- 2.8 mmol/45 min to 68.0 +/- 16.0 mmol/45 min (P less than 0.05). Loxiglumide failed to significantly influence bombesin stimulated amylase output (36.7 +/- 9.0 kU/45 min) and trypsin output (8.3 +/- 2.9 kU/45 min), but almost abolished bilirubin output (9.7 +/- 3.6 mmol/45 min) (P less than 0.05). Basal plasma CCK (2.4 +/- 0.1 pM) was not significantly influenced by loxiglumide (2.4 +/- 0.2 pM).(ABSTRACT TRUNCATED AT 250 WORDS)     

Accumulation of carbamoylphosphate-synthetase and phosphoenolpyruvate-carboxykinase mRNA in embryonic rat hepatocytes. Evidence for translational control during the initial phases of hepatocyte-specific gene expression in vitro

The aim of this study was to establish whether the initial accumulation of hepatocyte-specific proteins after hormone induction is regulated at the pretranslational and/or the translational level. To this end, mRNA molar concentrations were determined and compared with rates of protein synthesis from previous studies [van Roon, M.A., Charles, R. & Lamers, W.H. (1987) Eur. J. Biochem. 165, 229-234]. In vivo, carbamoylphosphate-synthetase mRNA starts to accumulate at day 17 of pregnancy. Phosphoenolpyruvate-carboxykinase mRNA starts to accumulate only just prior to birth. Embryonic day 14 (i.e. 8 days before the expected day of birth), livers were chosen to study the regulation of the initiation of hepatocyte-specific mRNA accumulation in vitro. Accumulation of carbamoylphosphate-synthetase and phosphoenolpyruvate-carboxykinase mRNA is regulated by the same hormones as accumulation of the respective proteins. The rate at which carbamoylphosphate-synthetase and phosphoenolpyruvate-carboxykinase mRNA molecules accumulate in cultured embryonic hepatocytes is relatively low, compared to that of postnatal hepatocytes. However, the increase of the rate of synthesis of carbamoylphosphate-synthetase and phosphoenolpyruvate-carboxykinase protein is even 3-6-fold slower than that of mRNA. This shows that initially mRNAs accumulate intracellularly to a relatively high concentration without being efficiently translated or translatable. Only after the mRNA concentration reaches a plateau of 72 h and 48 h respectively, the cellular capacity to synthesize the respective proteins increases. Therefore, the translational efficiency is certainly one of the major rate-limiting factors of the initial phases of expression of the hepatocyte-specific genes for carbamoylphosphate synthetase and phosphoenolpyruvate carboxykinase.     

Developmental and hormonal regulation of carbamoyl-phosphate synthase gene expression in rat liver: evidence for control mechanisms at different levels in the perinatal period

Carbamoyl-phosphate synthase gene expression is found to be primarily regulated by conditions that enhance hepatic glucocorticosteroid levels (hormone injections) and cyclic AMP levels (induction of diabetes). After birth, changes in the level of carbamoyl-phosphate synthase protein follow changes in the level of carbamoylphosphate synthase mRNA, suggesting a pretranslational control mechanism. In fetal rats, carbamoyl-phosphate synthase gene expression is regulated by the same factors as in adults. However, both the level to which carbamoyl-phosphate synthase mRNA can accumulate and the extent to which mRNA can be translated appear to be limited, indicating control mechanisms at the pretranslational and translational level. Finally, in the immediate postnatal period, a transient but pronounced decrease in the rate of degradation of carbamoyl-phosphate synthase protein may play a role in the accumulation of the enzyme.     

The fate of intraperitoneally injected carbon particles in cyprinid fish

Summary The lymphoid organs of rosy barb (Barbus conchonius) and carp (Cyprinus carpio) were investigated for their phagocytic uptake of carbon, after its intraperitoneal injection. Carbon handling was similar in both species. It was first detected in the lymphoid organs at 30 min after injection. During the first day, carbon was phagocytized by macrophages situated in the spleen within the ellipsoids and in the red pulp. In head and trunk kidney, carbon was found in macrophages scattered throughout the haemopoietic parenchyma, and in cells lining the blood sinuses. In the spleen, macrophages replete with carbon left the ellipsoidal structures and formed aggregates with pigment-containing macrophages from day 6 onwards. In all lymphoid organs, almost all carbon was ultimately concentrated in the melano-macrophage centres.     

Impaired local natural killer cell activity in human colorectal carcinomas

Summary The present study was undertaken to study natural killer (NK) cell activity in patients with colorectal cancer at peripheral and local levels. Mononuclear cells were isolated from uninvolved colorectal mucosa, tumor tissue and peripheral blood, and tested against the colon carcinoma cell line CaCo-2 and the erythroleukemia cell line K-562. Peripheral blood NK cell activity from the patients showed similar levels compared with healthy controls, whereas, mononuclear cells of tumor tissue were found to have a significantly decreased NK cell activity compared to the normal intestinal mucosa (P<0.01). No relation was found between the NK cell activity and the advancement of the disease according to the Duke's stage. Interferon- (IFN-) stimulated the NK cell activity of the mononuclear cells from blood, mucosa and tumor. However, the increase of NK cell activity after IFN- stimulation was lower in the tumor compared to the mucosa (P<0.02). The lectin, phytohaemagglutinin, increased the cytotoxicity of mononuclear cells from blood, mucosa and tumor to a similar level. These results suggest that patients with colorectal tumors exhibit a normal NK cell activity in peripheral blood and intestinal mucosa; however, a diminished NK cell activity exists at the tumor level. Although mononuclear cells isolated from the tumor have a normal response to lectin stimulation they show hyporesponsiveness to IFN- stimulation with regard to their NK cell activity.     

Regulation and functional significance of phospholipase D in myocardium

There is now clear evidence that receptor-dependent phospholipase D is present in myocardium. This novel signal transduction pathway provides an alternative source of 1,2-diacylglycerol, which activates isoforms of protein kinase C. The members of the protein kinase C family respond differently to various combinations of Ca²⁺, phosphatidylserine, molecular species of 1,2-diacylglycerol and other membrane phospholipid metabolites including free fatty acids. Protein kinase C isozymes are responsible for phosphorylation of specific cardiac substrate proteins that may be involved in regulation of cardiac contractility, hypertrophic growth, gene expression, ischemic preconditioning and electrophysiological changes. The initial product of phospholipase D, phosphatidic acid, may also have a second messenger role. As in other tissues, the question how the activity of phospholipase D is controlled by agonists in myocardium is controversial. Agonists, such as endothelin-1, atrial natriuretic factor and angiotensin 11 that are shown to activate phospholipase D, also potently stimulate phospholipase C- in myocardium. PMA stimulation of protein kinase C inactivates phospholipase C and strongly activates phospholipase D and this is probably a major mechanism by which agonists that promote phosphatidyl-4,5-bisphosphate hydrolysis secondary activate phosphatidylcholine-hydrolysis. On the other hand, one group has postulated that formation of phosphatidic acid secondary activates phosphatidyl-4,5-bisphosphate hydrolysis in cardiomyocytes. Whether GTP-binding proteins directly control phospholipase D is not clearly established in myocardium. Phospholipase D activation may also be mediated by an increase in cytosolic free Ca²⁺ or by tyrosine-phosphorylation.